Mount St. Helens is what kind of volcano, and what triggered the explosion? It is a stratovolcano that erupted due to the rapid release of trapped gases. When gases cannot easily escape from magma, the most powerful volcanic eruptions occur. The pressure increases until it can no longer hold itself together, at which point it explodes.
Stratovolcanoes like Mount St. Helens erupt relatively slowly, but they create more frequent small explosions and large amounts of ash than other types of volcanoes. They also often have very steep sides which cause them to collapse after an eruption has stopped changing their appearance. A good example of this type of volcano is Mauna Kea on Hawaii Island. Mauna Loa on the same island is a much larger volcano that does not have this characteristic - it releases gas rather than rock when it explodes.
Mountain ranges contain many different types of volcano, some with only light activity and others that are constantly emitting lava. There are also dormant volcanoes that occasionally show signs of life such as steam or hot springs. Dormant volcanoes may be located anywhere in the world but they are most common in areas where there has been recent geological activity because they need energy to keep going. Examples include California's Diablo Range and Oregon's Cascade Mountains.
The Pacific Ocean covers an area of about 2 million km2 (780,000 sq mi).
The subduction of the Juan de Fuca plate off the western coast of North America is responsible for Mount St. Helens and other volcanoes in the Cascades arc. Mount St. Helens has generated both spectacular explosive eruptions of volcanic tephra and rather calm lava outpourings during its rich and complicated 275,000-year history. The volcano's most recent eruption was on April 20, 1980, when the summit blast vaporized nearly 3 miles of forest and caused the mountain to collapse into itself with such force that it created a new crater more than 300 feet deep and 100 yards across.
After the blast, evidence showed that the majority of the volcano had been blown away, leaving only rock and soil behind. However, small amounts of material from the interior of the volcano were also ejected, including glass, sand, and small rocks. This material is called "tephra" and can be up to 25 feet thick over areas where the volcano has been blown out toward the ocean. Tephra covers much of the northern half of the volcano's former footprint today.
People have lived near Mount St. Helens for many years, but the area remains active volcano-wise. In fact, the last major eruption of Mount St. Helens was just over 250 years ago!
During an eruption, volcanoes produce gases that can become toxic if they are present in high concentrations.
The Cascade Volcanic Arc, a portion of the Pacific Ring of Fire, includes the volcano. Mount St. Helens is well known for its May 18, 1980, massive eruption, which was the bloodiest and most economically damaging volcanic event in U.S. history. The blast killed 57 people and destroyed much of the mountain's pristine forest.
In addition to the deaths, the eruption damaged or destroyed 435 buildings and poisoned some 150 people. It is estimated that the cost of damage from the explosion itself was $140 million and the cost of damage caused by pollution is as high as $1 billion per year.
Mount St. Helens has been called the "doorway to heaven" because of its distinctive appearance. A national monument since 2004, it is a popular destination for hikers and climbers.
St. Helens is an English name that means "martyr."
The mountain is located in Washington state, about 80 miles north of Seattle. Parts of the mountain collapsed due to erosion after the eruption, but most of the cone formed again after thousands of years. During an active period between 1750 and 1920, St. Helens had at least five major eruptions. The last major activity occurred in 1940 when a small amount of lava was emitted from two fissures on the northern slope of the mountain.
Mount St. Helens, a dacite volcano with a complicated magmatic system, is principally an explosive dacite volcano. The volcano developed through four eruptive episodes beginning at 275,000 years ago, and it was the most active volcano in the Cascade Range during the Holocene. It has been hypothesized that Mount St. Helens might have been responsible for the extinction of the Pleistocene megafauna in North America.
During its last eruption on April 20, 1980, the volcano destroyed 70% of the tree line and approximately 3,500 people lived in the path of the advancing lava flow. The death toll from this eruption is estimated to be 76 people; the majority of deaths were due to burning skin contact with molten rock that flowed into buildings where people lived.
In addition to the deaths, the eruption caused $1 billion in damage and created a new lake called Spirit Lake. The new lake covered much of the city of Spirit Rock, and it still exists today.
Since then, the volcano has remained inactive, but it can erupt again at any time. Scientists do not predict when this might happen again, but they say that if the mountain collapses there could be another devastating lahar (river) disaster like the one in 1917.
Mt. St. Helens is part of the Cascade Volcanic Arc, which extends from northern California to south-central British Columbia.
Helens. The eruptions of both volcanoes followed a similar pattern. Both volcanoes experienced earthquakes prior to the eruption. Both eruptions produced massive volumes of ash and volcanic debris, resulting in massive lahars that destroyed much of the surrounding land, cities, and residences. However, the eruption of Helens was more destructive than that of Pinatubo.
In May 1980, Mount St. Helen's erupted, producing a lahar (a mass of water and rock) that traveled down the mountain's flank at more than 20 miles an hour. It engulfed the town of Paradise, killing 57 people. The volcano then resumed activity, emitting gas and steam for several months more. In June 1992, Mount Pinatubo in the Philippines erupted, also producing a lahar that killed 121 people and destroyed communities along its path. After the eruption, rainstorms brought forth by the new atmosphere condition caused the death of thousands of plants and animals, including many species of birds and fish.
These two major eruptions proved that even though volcanoes tend to be quiet by nature, they can still be dangerous if they act up. With this in mind, scientists should continue to monitor these volcanoes closely to see if there are any changes in their behavior.